电偶合对钛合金TC4表面化学转化膜结构和性能的影响

发布时间：2018-06-22 12:03

本文选题：钛合金 + 电偶合　；参考：《山东大学》2017年硕士论文

【摘要】：金属表面磷酸盐化学转化膜致密、晶粒细小、性能优异,主要用于金属的腐蚀防护、涂装基底等方面。但目前,国内外对于钛合金表面磷酸锌制备的研究较少。本文在常温浸渍化学转化的基础上,重点研究了不同偶合材料、不同偶合面积比、不同接触面积比及时间对钛合金表面化学转化膜的影响,利用X射线衍射仪、热场发射扫描电镜、划痕仪及电化学工作站等技术手段系统的表征和分析化学转化膜的结构、形貌、结合强度、电化学性能,并对电偶合化学转化机制进行了初步探讨。结果表明未偶合条件下转化,无论时间长短,钛合金TC4表面没有化学转化膜形成,利用电偶合后基体表面均生成一层化学转化膜。转化膜的主要成分是磷酸锌(Zn3(P04)2·4H20)。TC4-MZG(Mg-1.75Zn-0.55Ga 镁合金)偶合体系得到的磷化膜层较致密,晶粒尺寸较小,无裸露基体现象。在所试验范围内,TC4-MZG面积比为1:1时,化学转化膜晶粒细小、致密、孔隙率小,其结合强度、耐腐蚀性能也最好。TC4-MZG偶合体系完全接触(接触比为1)时,转化膜晶粒尺寸明显减小,结合力达到24 N。电偶合能够开启化学转化反应,缩短转化时间,加速成膜速率。转化膜开始转化的时间约在15 s～30 s之间。延长转化时间能够促进晶粒数量增多和晶粒长大,但并不是时间越长转化效果越好。转化20 min时,化学转化膜均匀,致密,完全覆盖基体,继续增加转化时间,晶粒处于不断溶解和二次析出交替进行的状态。TC4-AZ91D偶合体系对化学转化膜物相、形貌影响明显。TC4-AZ91D偶合体系形成的化学转化膜是由Zn相和Zn3(PO4)2·4H20相构成,且随着偶合面积比的增大,Zn物相的含量越来越多。膜层由颗粒堆垛而成,这与其他偶合体系到的形貌不同。电偶合在化学转化中的成膜作用不是一种偶然现象。常温下利用电偶合在与钛合金具有类似性质的不锈钢、铜合金表面均能制备出一层均匀致密的转化膜。该转化膜主要是由磷酸锌(Zn3(PO4)2·4H2CO构成。电偶合能够缩短诱导时间,促进早期沉淀点的形成,制备出结构、性能优异的化学转化膜。通过研究电偶合成膜过程中的电位-时间曲线可知,化学转化膜的形成过程可以分为以下五个阶段:阳极表面氧化层及基体的溶解过程,阴极早期形核阶段,阴极晶核或新生晶粒的再溶解阶段,阴极晶粒的快速长大阶段,阴极转化膜的稳态生长阶段。
[Abstract]:Phosphate chemical conversion film on metal surface is compact, fine grain, excellent performance, mainly used in metal corrosion protection, coating substrate and so on. However, the preparation of zinc phosphate on the surface of titanium alloy is seldom studied at home and abroad. On the basis of chemical transformation of impregnation at room temperature, the effects of different coupling materials, different ratio of coupling area, different ratio of contact area and time on the surface chemical conversion film of titanium alloy were studied by X-ray diffractometer. The structure, morphology, binding strength and electrochemical properties of the chemical conversion films were characterized and analyzed by means of thermal field emission scanning electron microscope, scratch tester and electrochemical workstation. The mechanism of electrocoupling chemical conversion was also discussed. The results showed that no chemical conversion film was formed on TC4 surface of titanium alloy under uncoupled conditions, and a layer of chemical conversion film was formed on the substrate surface after electrocoupling. The main composition of the conversion film is zinc phosphate (Zn3 (P04) 24H20). TC4-MZG (Mg-1.75Zn-0.55Ga magnesium alloy) coupling system. When the area ratio of TC4-MZG to TC4-MZG is 1:1, the grain size of TC4-MZG film decreases obviously when its grain size is fine, compactness, porosity is small, its bonding strength and corrosion resistance is the best. TC4-MZG coupling system is in complete contact (contact ratio is 1). The binding ability was 24 N. Electric coupling can open the chemical conversion reaction, shorten the conversion time and accelerate the film forming rate. The conversion time of the film was about 15 s ~ 30 s. Prolonging the transformation time can promote the increase of grain number and grain growth, but the longer the transformation time is, the better the transformation effect is. During 20 min conversion, the chemical conversion film was homogeneous, compact, completely covered with the matrix, and the transformation time was increased. The grain was in the state of continuous dissolution and secondary precipitation alternately. TC4-AZ91D coupling system had a good effect on the phase of the chemical conversion film. The chemical conversion film formed by the coupling system of .TC4-AZ91D is composed of Zn phase and Zn3 (PO4) 24H20 phase, and the content of Zn phase increases with the increase of coupling area ratio. The film is made of granular stacking, which is different from the morphology of other coupling systems. The film forming effect of electric coupling in chemical transformation is not an accidental phenomenon. A uniform and compact conversion film can be prepared on the surface of copper alloy by electric coupling at room temperature on stainless steel with similar properties to titanium alloy. The conversion film is mainly composed of zinc phosphate (Zn _ 3 (PO _ 4) _ (24) H _ 2CO). Electric coupling can shorten the induction time, promote the formation of early precipitation point, and prepare chemical conversion film with excellent structure and performance. By studying the potential-time curves of the electrocoupling-forming process, the formation process of the chemical conversion film can be divided into the following five stages: the dissolution of the oxidation layer on the anodic surface and the substrate, and the early nucleation stage of the cathode. The phase of redissolution of cathode nucleus or new grain, the rapid growth of cathode grain, and the steady state growth of cathode conversion film.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

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